1. Field of the Invention
The present invention relates to an image recording equipment which records an image of written and/or pictorial information on a sheet of recording medium y laser exposure after removal of extraneous matter from the sheet of recording medium with an adhesive roller and a method of removing extraneous matter from the sheet of recording medium and, more particularly, to an adhesive roller that removes extraneous matter from the sheet of recording medium without causing separation of a sheet of recording medium from a rotary drum and/or winkles of the sheet of recording medium.
2. Description of Related Art
There are various recording equipments that record images of written and/or pictorial information such as a written document and a picture on sheets of recording medium (which is hereafter referred to as a recording sheets) by means of, for example, laser exposure. Such a recording equipment is generally made up of an image recording device, a sheet feeding device and a sheet carrying device. The image recording device operates to record images of written and/or pictorial information on recording sheets fed one by one from the feeding device and carried by the carrying device by means of, for example, laser exposure.
Referring to FIG. 9 that shows a fundamental configuration of one of image recording devices of this type, a image recording device includes a hollow cylindrical rotary drum 12 supported for rotation by a frame 14 and a recording head 16 supported for linear movement in a direction in parallel with a rotational axis of the rotary drum 12 on a pair of parallel guide rods 18. The recording head 16 scans a recording sheet (an image recording sheet or an image forming sheet) 1 closely contacted onto the rotary drum 12 by means of suction with a laser beam Lb. The rotary drum 12 is connected to and driven by an output shaft of a motor (not shown). Scanning operation of the recording head 16 is controlled by a control unit (not shown) according to data or scan signals provided for a given original. Further, synchronous operation of the image recording device including the rotary drum 12 and the recording head 16 is controlled by the control unit. As is well known in the art, the image recording device performs image formation through scamming a sheet wound around the rotary drum 12 in a primary scan direction that is the direction of rotation of the rotary drum 12 and a secondary scan direction that is the direction in parallel with the rotational axis of the rotary drum 12.
Although the sheet feeding device and the sheet carrying device which are not of direct importance to the invention are not shown in FIG. 1 because they are known in various forms and may take any form well known to those in the art, a brief description regarding them is hereafter provided for the purpose of enhancing an understanding of the invention. The sheet feeding device includes a sheet feeder tray or cassette in which a number of recording sheets are received, a pickup roller operative to pick up and push the recording sheets out of the sheet feeder cassette one by one to the sheet carrying device. The sheet carrying device, that is disposed between the sheet feeding device and the image recording device, carries the recording sheets one by one onto the recording drum 12 of the image recording device.
The recording sheet for image formation made through steps described below is prepared in a unit of, for example, five-recording sheets.
Referring to FIG. 10, one unit of recording sheets (recording sheet unit) 1 is made up of an image receiving sheet (one of recording sheets) 2 and four mono-color image forming sheets (another one of recording sheets) 3 prepared for four different colors, i.e. black (K), cyan (C), magenta (M) and yellow (Y), respectively. The image receiving sheet 2 comprises a sheet base 2a, a cushion layer 2b formed over the sheet base 2a and an image receiving layer 2c formed over the cushion layer 2b. The sheet base 2a may be made of a polyethylene terephthalate (PET)-based sheet, a triacetylcellulose (TAC)-based sheet, a polyethylene naphthalate (PEN)-based sheet, etc. The image receiving layer 2c receives an exposed portion of a pigment layer (which will be described later) of the mono-color image forming sheet 3. The cushion layer 2b functions to absorb differences in thickness of a stratified portion of pigment layers transferred onto the image receiving layer 2c. The image receiving sheet 2 is fed face-up to and is wound around the rotary drum 12 with the sheet base 2a closely contacted to the rotary drum 12.
The mono-color image forming sheet 3 comprises a sheet base 3a, a photothermal conversion layer 3b formed over the sheet base 3a, and a pigment layer 3c formed over the photothermal conversion layer 3b. The sheet base 3a is laser transmssive and may be made of the same material as the sheet base 2a of the image receiving sheet 2. The photothermal conversion layer 3b functions to convert radiant energy of laser light impinging thereon into thermal energy and may be of a general type of photothermal conversion material such as carbon, black materials, infrared absorption dyes and pigments, or materials that absorb light of specific wavelengths. The mono-color image forming sheet 3 is prepared for each of the different colors, black (K), cyan (C), magenta (M) and yellow (Y). When needed, the mono-color image forming sheet 3 is prepared for each of what are called special colors, such as gold and silver.
In the case where exposure for the formation of color image is achieved by forming four mono-color images in order of black (K), cyan (C), magenta (M) and yellow (Y), the recording sheet unit 1 includes the image receiving sheet 2, the black image forming sheet 3(K), the cyan image forming sheet 3(C), the magenta image forming sheet 3(M) and the yellow image forming sheet 3(Y) stacked in this order as one unit. In each recording sheet unit 1, the image receiving sheet 2 is put face-up and all the mono-color image forming sheets 3 are put face-down in the stack. A number of the recording sheet units 1 are received and stacked in the sheet feeder cassette. When recording an image on the recording sheet unit 1, the image receiving sheet 2 of an uppermost recording sheet unit 1 is fed to the image recording device at the first setout, and then the black, cyan, magenta and yellow image forming sheets 3(K), 3(C), 3(M) and 3(Y) of the uppermost recording sheet unit 1 are fed to the image recording device one by one in this order for sequential exposure. The same sheet feeding procedure is repeated for the following recording sheet units 1. The recording sheet unit 1 is known in various forms as disclosed in, for example, Japanese Unexamined Patent Publication Nos. 4-296594, 4-327982 and 4-327983 and may take any form well known to those in the art.
Recording a color image on the recording sheet unit 1 is performed the subtractive color process through four steps schematically shown in FIG. 11. Specifically, a color original, such as a written document or a color picture, to be reproduced is separated into three primary color images, i.e. cyan(C), magenta (M) and yellow (Y) images, in a well known manner.
After setting at least one recording sheet unit 1 in the sheet feeder cassette, the image receiving sheet 2 of the uppermost recording sheet unit 1 is picked up by the sheet feeding device and, then, carried face-up to the image recording device through the carrying device. The image receiving sheet 2 is wound around the rotary drum 12 with the sheet base 2a closely contacted to the rotary drum 12 by means of suction (Step I). Subsequently, the black image forming sheet 3(K) having a black pigment layer 3c of the uppermost recording sheet unit 1 is picked up by the sheet feeding device and, then, carried face-down to the image recording device through the sheet carrying device so as to be laid over the image receiving sheet 2 (Step II). In this state, the rotary drum 12 and the recording head 16 are driven in synchrinization in the primary and secondary scan directions according to data or scan signals provided for a given original to scan the black image forming sheet 3(K) with a laser beam Lb (Step III). As a result of the scan, the photothermal conversion layer 3b of the black image forming sheet 3(K) converts radiant energy of the laser beam into thermal energy in a distribution pattern in conformity with a black image of the given original. When peeling away the black image forming sheet 3(K) from the image receiving sheet 2 at the completion of scan, the black pigment layer 3c configured in the thermal energy distribution pattern is transferred to the image receiving sheet 2 (Step IV). As a result, a black image K of the given original is formed on the image receiving sheet 2.
These steps I to IV are repeated for the respective primary colors, i.e. cyan (C), magenta (M) and yellow (Y). As a result, the black, cyan, magenta and yellow images K, C, M and Y of the given original are formed on top of one another in this order on the image receiving sheet 2 and, in consequence, a color image of the given original is recorded on the image receiving sheet 2. The image receiving sheet 2 is peeled away from the rotary drum 12 at the completion of transfer of the black, cyan, magenta and yellow images K, C, M and Y. Thereafter, the image receiving sheet 2 is further processed in an image transfer processing device (not shown) to transfer the color image formed thereon onto a printing paper. In this way, a color image of the given original is reproduced on the printing paper.
During performing the process, it is possibly expected that solid foreign matter adheres to the surfaces of the image receiving sheet 2 and/or mono-color image forming sheets 3. As shown in FIG. 12 by way of example, if there is extraneous solid matter X such as dust or a particle between top layers 2c and 3c of the image receiving and mono-color image forming sheets 2 and 3, respectively, placed on top of each other, a void G occurs between them and, in consequence, causes the mono-color image forming sheet 3 to make a local convex deformation. The occurrence of void G is causative of an image defect such as a white or blank spot of an extent SI in an image formed on the image receiving sheet 2, and hence, of an image reproduced on a printing paper.
In light of these circumstances, studies are being made on how to prevent an occurrence of an image defect due to extraneous matter between these image receiving and image forming sheets 2 and 3. One of some solutions is the use of an adhesive roller operative functioning to remove extraneous matter from the image receiving sheet 2 and/or the mono-color image forming sheet 3 with adhesion at a location where at least one of sheet feeding device, the sheer carrying device and the image recording device is stationed. The adhesive roller is brought into contact with the image receiving layer 2c of the image receiving sheet 2 and the pigment layer 3c of the mono-color image forming sheet 3 during movement of them, or with the image receiving layer 2c of the image receiving sheet 2 wound around the rotary drum 12 of the image recording device.
In the case where the adhesive roller is installed to the image recording device so as to be brought into contact with the image receiving layer 2c of the image receiving sheet 2 wound around the rotary drum 12, if the adhesive roller is forced against the image receiving sheet 2 with a comparatively low contact pressure, it is difficult for the adhesive roller to remove extraneous matter of the image receiving layer 2c of the image receiving sheet 2. On the other hand, if the adhesive roller is forced against the image receiving sheet 2 with a contact pressure that is too high, the adhesive roller possibly breaks away the functional layer, i.e. the image receiving layer 2c and, in some cases, the cushion layer 2b from the sheet base 2a of the image receiving sheet 2, or possibly removes the image receiving sheet 2 itself from the rotary drum 12 against the suction when the adhesive roller is drawn apart from the image receiving sheet 2. Furthermore, in the case where the adhesive roller is installed in the path of movement of the sheets so as to establish contact with the image receiving layer 2c of the image receiving sheet 2 or the pigment layer 3c of the mono-color image forming sheet 3, the sheets are possibly wrinkled or undulated. In this instance, the image receiving sheet 2 often fails to wind itself closely around the rotary drum 12 due to wrinkles or undulation, and the wrinkled mono-color image forming sheet 3 fails to lay closely over the image receiving sheet 2 on the rotary drum 12 due to wrinkles or undulation.